As light-emitting elements that is capable of emitting light in a range from visible light into ultraviolet light, there is developed semiconductor light-emitting elements such as light-emitting diodes, semiconductor laser diodes and the like using single crystals of group III nitride semiconductors (AlxGa1-x)1-yInyN (0=x=1, 0<y=1).
Semiconductor laser elements have been realized in which a quantum well layer formed by sandwiching a semiconductor layer that has a small band gap and a film thickness of a few nanometers between two semiconductor layers having larger band gaps is used as a light-emitting layer. Semiconductor laser elements which allow a low threshold value operation by using a modulated doped structure as the active layer of a multiple quantum well (MQW) structure have also been proposed.
Conventionally, in InGaN based semiconductor lasers, the doping of the InGaN-MQW that acts as the active layer with impurities such as Si or the like has been uniformly performed in the barrier layers alone or well layers alone or in both types of layers (for example, see Re-published Patent WO98/19375). Alternatively, MQW in which the active layer is not doped, i.e., undoped MQW (that are not intentionally doped with impurities), have also been proposed (for example, see Japanese Patent Application Laid-Open No. 2001-7444).
In the past, even in semiconductor light-emitting elements with a quantum well structure, the operating current density has been high, and characteristics sufficient for practical use have not been obtained. Accordingly, there is a demand for a semiconductor light-emitting element which has a low operating current density, and which is suitable for continuous oscillation.